I doubt he is legally old enough to purchase alcohol. If he is old enough, boy he has some serious growing up to do & fast !!
I've never offered marijuana to non smokers & if I did extend out a joint their way it was because I didn't know & when he or she said no thanks well I would just leave it at that. Never push anything on anyone. If she wants to smoke then let her ask for it. Don't be persistent to get her to smoke. If she already turned it down once from you don't try anymore to get her to smoke. You'll lose her if you keep trying to get her to smoke & maybe even get your ass kicked.